This invention relates to water-in-oil emulsion blasting agent compositions having a single oxidizer salt. In another aspect, this invention relates to a water-in-oil emulsion blasting agent composition which is detonable under high heads of water and will propagate in rigid paper containers once detonated under such high heads of water. In still another aspect, this invention relates to an emulsion blasting agent which is inexpensive, powerful, simple to manufacture and resistant to sensitivity losses from impact that occur, for example, during shipment, even in extreme weather conditions.
In the past, there existed a need for a reliable and inexpensive nitro-carbo-nitrate (NCN) blasting agent that would function in wet boreholes under high heads of water. Previously the common practice was to use a packaged high density ammonium nitrate fuel oil (ANFO) blasting agent. Underwater use of the packaged ANFO often resulted in poor performance. Moreover, a suitable slurry product or emulsion that would meet the aforesaid requirements was not available. Bluhm, in U.S. Pat. No. 3,447,978, first disclosed use of water-in-oil emulsion type blasting agents. The emulsion blasting agents disclosed by Bluhm contain an aqueous solution of inorganic oxidizer salt that is emulsified as the dispersed phase within a continuous carbonaceous fuel phase, and a uniformly distributed gaseous component. These blasting agents require air for sensitization and possess poor water pressure tolerance. Bluhm basically relied on the presence of an occluded air phase or the addition of microbubbles to sensitize the blasting agent.
Wade, in U.S. Pat. No. 4,110,134, disclosed cap sensitive water-in-oil emulsion explosives using glass microspheres. Wade disclosed that there was a maximum detonation density of the explosive composition over which the composition would not be cap sensitive. The maximum detonation density was further disclosed to be a function of the amount of water, the type of oxidizer, and the amount of oil present in a composition. Wade did not teach or disclose a composition which would be non-cap sensitive and possess high water pressure tolerance.
Tomic, in U.S. Pat. No. 3,770,522, discloses that a water-in-oil emulsion can be formed of an aqueous solution of an inorganic oxidizing salt, a water insoluble carbonaceous fuel, a gas sensitizer which may be either occluded air bubbles or microballoons and a stearate salt selected from the class consisting of ammonium and alkali metal stearates as an emulsifier. Tomic asserts that the presence of the stearate salt causes the emulsion to have improved properties of water compatibility and pumpability and non-adherence to walls of packages.
Thornton, in U.S. Pat. No. 3,442,727, discloses a non-cap sensitive blasting agent which contains an aqueous phase of nitric acid and which can contain some oxidizer salts such as ammonium nitrate and a mono or di ester of phosphoric acid or a salt thereof used as an emulsifier for the nitric acid. Thornton does disclose that the composition can contain occluded air or gas imparting materials such as expanded perlite or hollow glass balls.
Cattermole, et al. in U.S. Pat. No. Re. 28,060, teaches that the addition of certain amine nitrate compounds to water-in-oil emulsion blasting agent compositions will assure that once such compositions are detonated, the explosion will propagate in a two or three-inch borehole.
Wade, in U.S. Pat. Nos. 3,715,247 and 3,765,964, discloses that water-in-oil emulsion explosive compositions can be prepared which retain all the advantages of the emulsion blasting agents but are cap-sensitive without the use of explosive ingredients. These two references disclose that such emulsion blasting agents can be rendered cap-sensitive by the addition of a detonation sensitizer or catalyst such as an inorganic metal compound of atomic number 13 or greater and strontium compounds.
Thus, heretofore a nitro-carbo-nitrate emulsion blasting agent having the capability of being detonable under high heads of water, the capability of propagating end-to-end in cardboard containers under high heads of water and having resistance to sensitivity losses from impact that occur, for example, during shipment, even in extreme weather conditions, was unavailable.